The Lib Dem leader also argued that any coalition with the party that finished second in the election — on most current projections Labour — would lack “legitimacy” with voters, who would question the government’s “birthright”.

In the clearest sign yet that he is contemplating a renewal of his 2010 coalition with the Conservatives, Mr Clegg told the Financial Times that Labour had been consumed by “frothing bile” towards his party for the past five years.

Mr Clegg said he would not join a coalition with Labour that required a deal with 40-50 SNP MPs to survive. Current polls suggest Ed Miliband, the Labour party leader, would need SNP support to secure a Commons majority.

“I totally rule out any arrangements with the SNP — in the same way I rule out any arrangements with Ukip — because there is no meeting point for me with one party that basically wants to pull our country to bits and another party that wants us to pull out of the EU,” Mr Clegg said.

“I would never recommend to the Liberal Democrats that we help establish a government which is basically on a life support system, where Alex Salmond could pull the plug any time he wants. No, no, no.”

Mr Clegg’s comments will come as a boost to David Cameron, who may be forced to turn to the Lib Dems to hold on to power in a hung parliament — the widely expected outcome of the election.

The Lib Dem leader, speaking en route to campaign in his Sheffield Hallam constituency, said he was “confident” of holding his seat and that his party would do “much better” than the 25-30 seats predicted by the polls.

There is no meeting point for me with one party that basically wants to pull our country to bits [the SNP] and another party that wants us to pull out of the EU [Ukip]

Nick Clegg, Lib Dem leader

Mr Clegg had strong criticisms of the Tories for their “socially regressive” plans for spending cuts and their “obsession” with Europe, which he claimed undermined Britain’s influence in the world.

But Mr Cameron will take comfort from Mr Clegg’s commitment that on May 8 he would begin exclusive coalition talks with the leader of the party with “the biggest mandate” in the Commons, which had “a right to seek a settlement”.

On most projections Mr Cameron is expected to win more seats than Mr Miliband, although the race is tight.

Only if those talks failed would Mr Clegg start negotiations with the leader of the smaller party in the Commons, but he fears that any so-called “coalition of the losers” could lack “legitimacy”.

“You cannot provide stability, you can’t take difficult decisions, if people are constantly questioning the birthright of a government,” he said.

Labour officials said it was well known that Mr Clegg and allies such as Danny Alexander and David Laws favoured another coalition with the Tories but that “it doesn’t necessarily reflect the views of the Lib Dems”.